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This page is divided into 4 sections. The first section describes how to set up the model (PCF structure + simulation parameters). Sections 2 and 3 describe how to perform Modal analysis and Frequency analysis, and section 4 demonstrates how to use the built-in parameter sweeping tool to study the loss as function of bending.

 

In this topic

Set up model

Modal analysis

Frequency analysis

Bend analysis

Set up model

The physical structures to be modeled are created using the STRUCTURES tab in the Layout Editor. The first step is to create the fiber with the air holes.

 

Begin by starting MODE.  You can save the MODE Simulation Project file (extension *.lms) at any point in this process. To do so, choose SAVE in the FILE menu.

Press the MATERIAL DATABASE button icon_materials and add a new sellmeier material with the following properties:

section

property

value


name

Corning 7980 Silica


color

dark blue

Material Properties

A0

1


B1

0.68374


C1

0.00460353


B2

0.420324


C2

0.0133969


B3

0.585027


C3

64.4933

Press on arrow on the STRUCTURES button icon_structures and select a CIRCLE from the pull-down menu. Set the properties of the circle according to the following table.

tab

property

value


name

fiber

Geometry

x (μm)

0


y  (μm)

0


z  (μm)

0


z min (μm)

-0.5


z max (μm)

0.5


radius (μm)

300

Material


Corning 7980 Silica

Press on arrow on the COMPONENTS button icon_components and select PHOTONIC CRYSTALS from the pull-down menu. This will open the object library window.

Select HEXAGONAL LATTICE PC H-CAVITY from the list and press the INSERT button.

Set the properties of the PC Cavity according to the following table.

tab

property

value


name

pc cavity

Properties - Origin

x (μm)

0


y (μm)

0


z (μm)

0

Properties - User Properties

material

etch


H number

1


z span (μm)

1


n side

6


a (μm)

23.2


radius (μm)

5.8

Press on the SIMULATION button icon_mode_simulation to add an EIGENMODE SOLVER simulation region. Note that if your button does not look like the button to the left, you will need to press on the arrow to get the simulation region. Set the properties according to the following table.

tab

property

value

General

solver type

2D Z normal

Geometry

x (μm)

0


y (μm)

0


z (μm)

0


x span (μm)

12 * 23.2


y span (μm)

12 * 23.2 * sin(60*pi/180)

Mesh settings - Number of mesh cells without override regions

mesh cells x

60


mesh cells y

60

Boundary conditions

x min bc

PML


x max bc

PML


y min bc

Symmetric*


y max bc

PML

Press the Zoom EXTENT icon_zoomextent button to resize the view in the Layout Editor.

 

Modal Analysis

Select the ANALYSIS tab with the RUN ACTIVE SIMULATION button icon_run.

Under the Modal analysis tab, enter the following parameters:

tab

property

value

Modal analysis

wavelength (um)

1.55


number of trial modes

20


search

in range


n1

1.44399 (max n)


n2

1.4

Click the MESH STRUCTURE button to see the meshed PCF.

Press the CALCULATE MODES button. Once you see a few modes appear in the index table, press the STOP button on the progress window.

Once we determine the effective index of the fundamental mode to be near 1.4436, return to the layout editor by LAYOUT button icon_switch. Select the MODE object and set the number of mesh cells in x and y to be 120. This will make the simulations slower, but more accurate.

Back to the MODAL ANALYSIS tab, now select the SEARCH NEAR N option, uncheck use max index, and enter the effective index of 1.4436.  Then press the CALCULATE MODES button.

In addition to the Modal Analysis tab, one can also view the calculated modes using the Visualizer. In the Object tree as shown below, under the Eigensolver simulation region there is a EigensolverDataGroup called "data", which contains a material monitor as well as all the modes in the current mode list. One can then right click on the object and choose to Visualize the different datasets corresponding to each object.

 

mode_gs_pcfibre_visualize_mode_zoom76

 

For example, one can visualize the Electromagnetic fields of mode1:

 

mode_gs_pcfibre_visualize_mode2_zoom71

 

Frequency Analysis

Under the Frequency analysis tab, select the mode that you want to track (by clicking on it in the mode table), and enter the following parameters:

tab

property

value

Frequency analysis

stop wavelength (um)

1.4


number of points

10


number of test modes

3


track selected mode

on


detailed dispersion calculation

on

Click on the FREQUENCY SWEEP button to begin the scan. The scan will take about a minute.

To plot the calculated dispersion as a function of wavelength, select the FREQUENCY PLOT tab in the bottom righthand corner of the frequency analysis window. Then select "Dispersion" in the plot pull down menu. The plot can be seen above the frequency plot tab. If you press the PLOT IN NEW WINDOW you will get a new window.

To determine the fraction of the total measured dispersion results from the waveguide geometry, as opposed to bulk material dispersion, we need to return to the layout editor and change the material properties of the fiber.  Return to the layout editor by clicking the LAYOUT button icon_switch, MODE will automatically close the Analysis Tab.  

Select the fiber structure, set the material from "Corning 7980 Silica" to  "<Object defined dielectric>" and set the INDEX to 1.444, rerun the frequency sweep.

 

Bend Analysis

In the following step of analyzing the photonic crystal fiber, we examine how the total loss in a 90 degree bend varies as a function of the radius of curvature. Before running the sweep, switch back to LAYOUT and set the material for the fiber back to "Corning 7980 Silica" and recalculate the modes. To perform a series of simulations to investigate the effect of systematic changes on cavity performance, it is convenient to take advantage of the built-in parameter sweep tool in MODE. There are 3 steps to setting up the bend analysis parameter sweep:

 

Step 1: Make data available to parameter sweep

We are interested in obtaining the loss from the fundamental mode, but the mode solver generally finds multiple modes. In order to keep track of the desired mode, we need to store a reference copy of the fundamental mode as a D-CARD (the D-CARD is a convenient data storage system which allows you to define, analyze, and transport data between analysis routines and applications).  Within the MODE LIST, highlight the fundamental mode, right click and "Add selected modes to global deck", a D-CARD with the default name "global_mode1" will be created.  Double click on this D-CARD and change the name to "FUND" (note that the name should be entered in capitals).

 

mode_gs_pcfibre_deck_zoom51

 

Next, we want to save the loss of the fundamental mode at each bend radius setting.

 

mode_gs_pcfibre_loss_sweep1_zoom89

 

Switch back to LAYOUT and edit the MODE data group by right clicking on the object with your mouse. Select the Edit object option from the list as shown in the figure above.

In the Analysis->Variables tab click the bottom ADD button. This will add a result which the data group can give to the parameter sweep. Rename the result to "loss" as shown in the bottom left window.

Switch to the Analysis_>Script tab shown in the right part of the image below. Then add the following lines of script commands which will add data to the "loss" result once a simulation has run. Press OK to save your changes.

 

fund = bestoverlap("FUND"); # find the mode that best overlaps with "FUND"

loss = getdata(fund,"loss"); # save the loss result for this mode

 

mode_gs_pcfibre_loss_sweep2_zoom37

 

Step 2: Create a sweep

Open the Optimization and Sweeps window using the VIEW menu at the top of the graphical user interface, or by right clicking on the top title bar of the MODE GUI.  

Press on the CREATE NEW PARAMETER SWEEP button icon_sweep to add a new sweep to the simulation. Right click on the parameter sweep and choose to edit the parameter sweep. Set the properties according to the following screenshot. Notice that the only results you can chose are the results which are seen in the screenshot of the Analysis->Variables tab above.

Here, the values specified for "roc" (radius of curvature) follow the equation roc = 2/linspace(1,5.5,10)^2, so we select "Values" as shown below and enter each value one by one. If we wish to sweep the parameter in evenly spaced intervals, it would be easier to select "Range" and enter the Start/Stop values instead.

 

mode_gs_pcfibre_loss_sweep3_zoom54

 

Step 3: Run the sweep and plot the data

In the Modal analysis window, select the "bent waveguide" option under modal analysis, and click "Calculate Modes". This will enable the sweep to change the value for the bend radius.

Press the RUN SWEEP button icon_run_sweep in the Optimizations and Sweeps Window to run the sweep.

Just like in Modal Analysis, we can use the Visualizer to plot the results.

 

mode_gs_pcfibre_loss_sweep4_zoom84

However, here it is more useful to plot (instead of just loss), since we want to determine the loss in a 90 degree bend. Note that this is the actual bend angle, not the bend orientation.

 

To do this, open the script prompt window using the VIEW menu at the top of the graphical user interface, or by right clicking on the top title bar of the MODE GUI. Copy and paste the following commands into the script prompt and press ENTER on the keyboard to execute them.  

 

result = getsweepresult('sweep','loss');

loss = result.loss;

roc = result.roc;

plot(roc*1e3,loss*roc*pi/2,"radius (mm)","loss in 90 degree bend (dB)","","logplot");

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